Advantages of Intermittent Flow Control Schemes on the Purdue Hog Cooling Pad for Mitigating Heat Stress in Lactating Sows

The Purdue hog cooling pad has previously been demonstrated to adequately mitigate heat stress in lactating sows by conductively transferring heat from the sow to cold water running through the cooling pad. The cooling effectiveness describes how much heat is removed per liter of water flushed through the cooling pad. Past studies indicated that intermittent flow of the cooling water could achieve greater cooling effectiveness than continuous flow systems. An electronic control system was implemented on the current cooling pad design to allow for automated control of a solenoid valve based on a preprogrammed flush condition. The control schemes were categorized into two groups: temporal and temperature threshold. The temporal schemes opened the solenoid for 30 seconds before closing it for 3, 6, or 9 minutes. The temperature threshold control schemes utilized feedback from temperature probes embedded beneath the surface of the cooling pad to open the solenoid for 30 seconds when a surface temperature of at least 28.0C 29.5C, or 31.0C was detected. The temperature threshold control schemes achieved greater heat transfer rates (348, 383, 268 W) versus the temporal control schemes (324, 128, 84 W). The cooling effectiveness for all control schemes ranged from 46.6 to 64.7 kJ/L. Intermittent flow control schemes did achieve greater cooling effectiveness than continuous flow systems from previous studies, but they did so at lower heat transfer efficiencies.